Methods for ascertaining the harmonic components of analog electrical signals are known. In this case, the analog signal is sampled and digitized at a sampling frequency, for example, so as then to use fast Fourier transformation FFT to calculate the Fourier transformation for the signal. This requires a fixed number of samples to be ascertained per period of time. For this reason, a fundamental frequency changing over time requires the sampling frequency to be continually tracked. In addition, the sampling system needs to be in tune with the maximum sampling frequency.